package com.example.rsalogindemo.util;

import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;

import javax.crypto.Cipher;

public class RSAEncrypt {
    public static void main(String[] args) throws Exception {
        Map<Integer, String> keyMap = genKeyPair();
        String message = "heheheh";
        String pulbicKey = keyMap.get(0);
        String privateKey = keyMap.get(1);
        System.out.println("随机生成的公钥为:" + pulbicKey);
        System.out.println("============================================");
        System.out.println("随机生成的私钥为:" + privateKey);
        System.out.println("============================================");
        String messageEn = encrypt(message, pulbicKey);
        System.out.println("加密后的字符串为:" + messageEn);
        System.out.println("============================================");
        String messageDe = decrypt(messageEn, privateKey);
        System.out.println("还原后的字符串为:" + messageDe);
    }

    /**
     * 随机生成密钥对(返回公钥和私钥)
     */
    public static Map<Integer, String> genKeyPair()
            throws NoSuchAlgorithmException {
        // KeyPairGenerator类用于生成公钥和私钥对，基于RSA算法生成对象
        Map<Integer, String> keyMap = new HashMap<Integer, String>();
        KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
        // 初始化密钥对生成器，密钥大小为96-1024位
        keyPairGen.initialize(1024, new SecureRandom());
        // 生成一个密钥对，保存在keyPair中
        KeyPair keyPair = keyPairGen.generateKeyPair();
        // 得到私钥
        RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
        // 得到公钥
        RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
        String publicKeyString = new String(
                new sun.misc.BASE64Encoder().encode(publicKey.getEncoded()));
        // 得到私钥字符串
        String privateKeyString = new String(
                new sun.misc.BASE64Encoder().encode((privateKey.getEncoded())));
        /*
         *  将公钥和私钥保存到Map
         *  0表示公钥
         *  1表示私钥
         */
        keyMap.put(0, publicKeyString);
        keyMap.put(1, privateKeyString);
        return keyMap;
    }

    /**
     * RSA公钥加密
     *
     * @param str       加密字符串
     * @param publicKey 公钥
     * @return 密文
     * @throws Exception 加密过程中的异常信息
     */
    public static String encrypt(String str, String publicKey) throws Exception {
        // base64编码的公钥
        byte[] decoded = new sun.misc.BASE64Decoder().decodeBuffer(publicKey);
        RSAPublicKey pubKey = (RSAPublicKey) KeyFactory.getInstance("RSA")
                .generatePublic(new X509EncodedKeySpec(decoded));
        // RSA加密
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.ENCRYPT_MODE, pubKey);
        String outStr = new sun.misc.BASE64Encoder().encode(cipher.doFinal(str
                .getBytes("UTF-8")));
        return outStr;
    }

    /**
     * RSA私钥解密
     *
     * @param str        加密字符串
     * @param privateKey 私钥
     * @return 铭文
     * @throws Exception 解密过程中的异常信息
     */
    public static String decrypt(String str, String privateKey)
            throws Exception {
        // 64位解码加密后的字符串
        byte[] inputByte = new sun.misc.BASE64Decoder().decodeBuffer(str);
        // base64编码的私钥
        byte[] decoded = new sun.misc.BASE64Decoder().decodeBuffer(privateKey);
        RSAPrivateKey priKey = (RSAPrivateKey) KeyFactory.getInstance("RSA")
                .generatePrivate(new PKCS8EncodedKeySpec(decoded));
        // RSA解密
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, priKey);
        String outStr = new String(cipher.doFinal(inputByte));
        return outStr;
    }
}
